Few people think about fins as being important equipment. They are hidden away under your board so you see them briefly when setting up and then on water you only notice them when they become loose or fall off. A board with no fin is barely controllable and the usual stage before that when a loose fin pivots and hangs below the board is when you first notice something is badly wrong. For this reason its worth always carrying a spare fin on a long paddle or is a group of you are going out together as a group member with a finless board will not be able to keep up.
Quick release fins which push in and don’t require a screw to hold them in place are ideal as a spare fin. You can use them as your main fin but beware they can be quite easily dislodged by a stone on a shallow river bed (for example when you are launching backwards). Not great as they are quite expensive.
Some boards have longer fin boxes which enable the fin to be positioned slightly further forward or backward. Positioning towards the back makes the board easier to track in a straight line but slightly harder to turn.
All fins cause drag but to some extent this is welcome because the drag keeps the front of the board lined up with the back. A longer or wider fin will increase drag but also keep the board more stable. A thicker fin will also increase drag but it will be stiffer. Carbon fins achieve stiffness without thickness – and they are also lighter although the weight saving is marginal and they are expensive.
There are various fin shapes, directional swept back, upright and general all round are the main categories. An upright fin with a small area is good for speed but it will not track (keep the board going in a straight line) as well as a swept back fin which having more or its surface area towards the back of the board assists tracking. Uprights also collect weed and debris more easily so on canals or weed choked rivers and lakes they are a liability. One small strand of weed creates a lot of drag and constantly stopping to clear weed is no fun so s swept back fin will reduce your journey time and increase enjoyment.
Multi-fin set ups
On flat water a single fin is best as its all about going in a straight line, stability and minimising drag. On fast moving, turbulent water where changes of direction need to be frequent them multi-fin arrangements work best. This set-up also allows for smaller fins which are less likely to ground and break when they hit rocks. Surf SUP boards often have three fins or more and whitewater specific boards similarly.
The most common fin type is the American Box Fin with a screw and backplate attachment but there other options with slot in fins not requiring a screw. These have the advantage of being easier to take on and off with cold hands – with no screw to drop and lose – but the range of fins for these is limited and tends to be mainly basic and cheap.
Most practical fins for the Tideway
We have tried most types fins on the Tidal Thames and most have worked well. Around low tide long fins can be a liability as the river bed is uneven and grounding is always a possibility. However, the extra stability from a longer fin may be welcomed by some paddlers so the need to keep a lookout for shallows when near the shore is an inconvenience worth accepting.
While carbon fins are good, they are fragile and more easily damaged by rocks. Plastic flexi fins are durable and inexpensive. Not the best performance but good enough for most and the flexibility also protects your fin box if your board is dropped or jumped on.
As with boards and paddles its best to try a few to see which you like best. A few spare fins will always be useful so getting it right first time is no big deal.